This invention relates generally to rotatable apparatuses and specifically to a rotatable apparatus having a pair of rotatable members joined by a stress dissipating structure.
The primary function of a gear is to transmit power from a power generating source to an operating device. This is achieved through the intermeshing and continuity of action between the teeth of a driving gear which is associated with the power source and the teeth of the mating gear which is associated with the operating device. Since a gear is a rotating body, a state of dynamic equilibrium must be attained. Therefore, to be in dynamic equilibrium all of the reactions from the rotating gear must be neutralized by equal and opposite forces supporting the gear shaft.
Traditional gear design comprises a central hub, a web extending radially outward therefrom which is, in turn, peripherally bordered by an integral radial rim having geared teeth thereupon. Gear failure can occur if manufacturing tolerances, material type, and gear design are not matched to the service application. Furthermore, since gears have historically been manufactured from a single homogeneous material, the bulk rigidity and strength of the web is generally greater than or equal to that of the hub and rim. Thus, torsional stresses created through start-up, shut-down, overload, or through cyclical fatigue are localized in the teeth and hub areas. As a result, gears typically fail at the root of the teeth or in the hub region. Such failures include excessive wear, plastic flow or creep, tooth bending fatigue, contact fatigue (pitting and spalling), thermal fatigue, tooth bending impact, tooth shear, tooth chipping, case crushing, torsional shear and stress ruptures. Many of these failures are due primarily to overload, cycling fatigue, and/or start-up and shut-down rotational shock referenced above that is especially prevalent in gears that perform in non-constant rotation service applications.
An alternative gear design that has been used is a compliant gear having a rigid one-piece hub and web, and a separate rim member with a rubber-like insert or ring located between the outer radial edge of the web and the inner radial edge of the rim. An example of this configuration is disclosed in U.S. Pat. No. 2,307,129 entitled "Shock Proof Gear", issued to Hines et al. on Jan. 5, 1943. Although this rubber-like insert is supposed to dampen audible vibrations and somewhat reduce resultant stresses within the gear, under load the rim is capable of compressing one side of the rubber-like insert such that the rotational axis of the rim could become axially offset from the rotational axis of the hub. This misalignment can cause partial or complete disengagement of the gear teeth of the compliant gear from those of its mating gear. In addition, gears having this type of rubber-like insert strictly between the web and the rim are subject to the rim torquing away from the hub in a transverse direction normal to the direction of rotation. Under load this transverse movement may also cause misalignment of the mating gear teeth which will localize stresses upon distinct portions of each tooth. Moreover, the hub and rim may not provide an adequate attachment, and thus force transfer, surface for the rubber-like insert in extreme torque situations. A similar design using elastomeric laminates with a shim therebetween is disclosed in U.S. Pat. No. 4,674,351 entitled "Compliant Gear", issued to Byrd on Jun. 23, 1987.
Another compliant rotating member configuration is disclosed in FIG. 8 of U.S. Pat. No. 3,216,267 entitled "Rotary Motion Transmitting Mechanism For Internal Combustion Engines And The Like", issued to Dolza on Nov. 9, 1965. That sprocket/gear design contains a stamped cup-shaped hub which has an outward radially extending flange and a cushioning member fully attached to the side thereof. The rim of the sprocket/gear has a generally L-shaped cross section with the radial inward leg being fully attached to the opposite side of the cushioning member. In that design there are gaps between the outer circumference of the cushioning member and the inside radial surface of the rim and also a gap between the radially inward surface of the cushioning member and the radially outward horizontal edge of the cup-shaped hub section. While the sprocket/gear is designed to maintain angular torsional rigidity while having radial flexibility, under load the rim of the sprocket/gear may become elliptical and thus encroach upon the gaps created above and below the cushioning member. Moreover, the rotational axis of the rim may also become offset from the rotational axis of the hub under working conditions.
It is also known to provide a sunroof motor with a conventional gear having a unitary polymeric rim, offset web and hub. This gear further has a receptacle and an inner set of rim channels for receiving a metallic cup in an interlocking fashion. A Belleville washer frictionally rides against an outer surface of the metal cup and is interlocked to a pinion shaft. The gear is also journalled freely about the shaft. The amount of frictional force exerted by the Belleville washer against the cup is controlled by the amount of torque supplied to a pinion shaft engaging nut; thus, the Belleville washer acts as a clutch mechanism. However, this traditional sunroof motor is not provided with a rotational stress dissipating structure beyond the coaxial Belleville washer.
Furthermore, many conventional clutches employ rotation dampening devices and spring biasing devices. For instance, reference should be made to the following U.S. Pat. No. 5,333,713 entitled "Friction Clutch" which issued to Hagnere et al. on Aug. 2, 1994; U.S. Pat. No. 5,322,141 entitled "Damped Driven Disk Assembly" which issued to Szadkowski on Jun. 21, 1994; U.S. Pat. No. 5,310,025 entitled "Aircraft Brake Vibration Damper" which issued to Anderson on May 10, 1994; U.S. Pat. No. 5,308,282 entitled "Pressure Plate for a Vibration Damper Assembly having Built-In Lash" which issued to Hansen et al. on May 3, 1994; U.S. Pat. No. 5,273,145 entitled "Hydraulic Clutch Control Means, In Particular For A Motor Vehicle" which issued to Corral et al. on Dec. 28, 1993; U.S. Pat. No. 5,186,077 entitled "Torque Variation Absorbing Device" which issued to Nakane on Feb. 16, 1993; U.S. Pat. No. 5,161,660 entitled "Clutch Plate with Plural Dampers" which issued to Huber on Nov. 10, 1992; U.S. Pat. No. RE 34,105 entitled "Internal Assisted Clutch" which issued to Flotow et al. on Oct. 20, 1992; and U.S. Pat. No. 4,996,892 entitled "Flywheel Assembly" which issued to Yamamoto on Mar. 5, 1991; all of which are incorporated by reference herewithin. While many of these clutch constructions recognize an unsatisfied need for rotational stress reduction devices therein, further improvement in performance, cost and assembly would be desirable. For example, the rotationally oriented compression springs utilized in some of these constructions can be easily overcompressed beyond their elasticity limit, thus, leading to poor subsequent performance. By themselves, these compression springs are not well suited for repeated, high load, full compression.